Telephone system



March 13, 1934. BELAS 1,950,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 1 Francis Tafinck Balas 15 Sheets-Sheet 2 Emil-F Francis TE'HQCK Bela: 7

F. T. BELAS TELEPHONE SYSTEM Filed Mal-ch25, 1931 March 13, 1934.

March 13, 1934. F. T. BELAS 1,950,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 3 Iml 1m Francis Ta'flu 12K Belas March 13, 1934. T. BELAS 1,950,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 5 E. 0 o O o 48 a O idjog w m a Toll Francis Tilluck Bela;

March 13, 1934. F. T. BELAS 1,950,877

TELEPHONE SYSTEM I Filed March 25, 1931 15 SheetsSheet 6 If E 22 s TL L... a; l CL R 11 I Z a r T N 4, r J) J) 0o E N A D L 5 g i i Inuenimr Francis Ti'fic: :K Bah:

March 13, 1934. F. T. BELAS TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet '7 3: Mi M K 5 Nm 8 11mm- Francis T511: :K E: 2115 ww March 13, 1934. BELAs 1,950,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 8 Francis Tit lick B Ill March 13, 1934. F. T. BELAS TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 9 Francis Tiflmck E121 15 Sheets-Shet 10 March 13, 1934. F. T. BELAS TELEPHONE SYSTEM Filed March 25. 1931 9 m m 2 m QE i u g m QQE gm @E c: LI

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March 13, 1934. F. T. BELAS TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Shet 11 Imam- Francis TaTflc ck B2125 March 13, 1934. F. T. BELAS 1,950,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 12 I'TTL'L'rTE'r'EEF Francis Tiflmck Belas March 13, 1934. F. T. BELAS 1, 0,877

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet 13 5 Q &

ITLUEntDr' Francis T'HncK Ea'las March 13, 1934.

F. T. BELAS TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet l4 March 13, 1934. F. T. BELAS 1,950,377

TELEPHONE SYSTEM Filed March 25, 1931 15 Sheets-Sheet l5 acl Inventor Francis T EHEIEK B32185 Ell Patented Mar. 13, 1934 UNETE STATES PATENT FFICE TELEPHONE SYSTEM ware Application March 25, 1931, Serial No. 525,18.? in Great Britain March 27, 1930 30 Claims.

The present invention relates to telephone systems and has for its object the provision of a new and improved train of automatic switches for use in such systems.

The invention is concerned with the provision of arrangements for enabling a toll operator to establish connection with a line which is already engaged in a local connection. This is effected by providing combined local and toll final selectors with two sets of line wipers and arranging the connections in the subscribers line circuit so that the subscribers line is always taken into use over a particular set of wipers so that when a toll operator desires to disconnect the wanted subscriber from a local. connection, the subscribers line is disconnected from the local switches but remains accessible to the other set of wiper of the final selector switch.

According therefore to one feature of the invention in a telephone system a wanted line is accessible over twcipaths one of which is accessible only to privileged parties the other path being disconnected when the path accessible only to privileged parties taken into use.

According to a further feature of the invention in a telephone system having local and toll calls extended to a wanted line over automatic switches a relay individual to the wanted line is adapted to be controlled from the toll board to effect the disconnection of the wanted line from automatic switches over which the wanted line is engaged in a local call.

According to a further feature of the invention in a telephone system having subscribers lines accessible over one route to non-privileged parties and over a different route to privileged parties a connection established over the second route automatically prevents subsequent connections being extended to a line over either route.

According to a still further feature of the invention in a telephone system a connector switch adapted to be used in both toll and local connections is provided with two sets of wipers one set of which is accessible to calling subscribers whilst the other set is accessible only to operators.

These and other features of the invention will be better understood from the following description of a preferred embodiment of the invention, taken in conjunction with the accompanying drawings comprising Figs. 1 to 14 which should be arranged as shown in the key sheet Fig. 15 to form a complete circuit.

Fig. 1 shows the subscribers line cut-off and toll breakdown relay circuit arranged for toll breakdown and also suitable for use when it isrequired to provide the arrangement for disco'nnee-ting the finder switch if the calling subscriber does not dial within a predetermined period.

Fig. 1c shows the subscribers line circuit without this latter facility but arranged for toll breakdown and is intended to replace Fig. 1 when toll breakdown only is required.

2 shows a typical finder switch,

Fig. 3 shows a typical local first selector possessing a digit absorbing feature,

Fig. 4 shows a combined regular and toll final selector,

Fig. 5 is meant to illustrate the called subscribers line cut-off and toll breakdown relays and is substantially the same as Fig. 1,

Figs. 6 '7 are similar and show the finder distributor circuit for A and B groups respectively, and also includes the emergency changeover arrangement in case either distributor switch should become faulty,

Fig. 8 shows a typical incoming or toll selector not including the digit absorbing feature,

Fig. 9 shows an auto-to-auto repeater utilized in the repeating of impulses to the selectors at a distant exchange,

Fig. 10 shows the main and extended alarm relay group,

Fig. 11 shows a relevant portion of a toll operators cord circuit,

The left-hand half of Fig. 12 shows the delayed alarm circuit arranged for a 36 seconds delay and used in connection with the finder switches, the right-hand half of Fig. 12 shows the release alarm supervisory equipment,

Fig. 13 shows a delayed alarm equipment arranged for a three minute delay used in connection with the final selectors and 14 shows the equipment utilized in the generation and distribution of ringing and tones.

Referringnow to the assembled circuit, when a subscriber desires to originate a call he will lift his receiver from the switch hook in the usual manner thereby completing a circuit across the conductors l0 and 11, Fig. 1, for operating relay LR over its upper winding. Relay LR in operating at armature Zrl removes earth from the conductor 13 to mark the appropriate position in the finder bank multiple, at armature lr2 extends earth by way of the resting armature col over conductor 14 which represents the finder start common to operate the start relay A in the A group finder distributor circuit, 7. The operation of the finder distributor is described in detail in British Patent No. 333,182 from which it will be seen that it includes arrangements for setting a second finder in operation if the first finder is not connected to the calling line within a predetermined period. One difference that should be mentioned however is that the finders in the present application are 100 point finders and are not arranged to give preferential service. Each finder is permanently linked with a first selector which is of the two directional type familiar to those skilled in the art, with the addition of an extra relay F and normal post springs NP for causing the selector to drop back from certain levels. In addition there is a common delay set, Fig. 12, provided for each group of finders for the purpose of giving an alarm and disconnecting the calling line if the calling subscriber fails to dial within a predetermined period. This is accomplished in the following manner.

When the finder which has been allocated by the distributor has found the calling line in the manner described in the previously mentioned patent and switched through to its associated local first selector, Fig. 3, relay 2A of the latter switch operates over the circuit including the calling subscribers instrument and at armature 2a1 extends earth from resting armature 1723 to operate relay 2B.

In addition to performing functions which will be described later relay 23 at armature 2bl completes the circuit from earth to conductor 23 and thence via resting armature 2101, operated armature hl, resting armature 2p2, wiper 3a and bank contact associated with the calling subscriber, conductor 13, operated armature Zrl, lower winding of relay LR and winding of relay CO in series to battery. Relay LR holds over this circuit and. relay CO operates, at armature col removing earth from the finder start common conductor 14. and at armatures 002 and 003 clearing the talking conductors 24 and 25 of attachments. Armatures 002 and 003 also have other functions to be described later. Relay 2B, Fig. 3, also at armature 2b2 earths conductor 15 to operate the motor start relay MS, Fig. 8, at armature 2b3 prepares the impulsing circuit for the vertical magnet 2VM and at armature 2M connects up conductors 26 and 27 in order to complete the circuit of relay SP, Fig. 2, which operates frombattery, upper winding of relay SP, conductor 26, operated armature 2194, conductor 27, resting armature e103, conductor 28, home contact of bank 2 of delayed alarm rotary switch DAR, Fig. 12, wiper 2b to earth. Relay SP at armature spl locks up in a circuit extending from battery upper winding of relay ZP, operated armature spl, lower winding of relay SP, conductor 29, over operated armature 2196 to earth. Armature 8272 prepares a circuit for the lower winding of relay ZP. Relay MS, Fig. 8, in operating at armature msl provides earth over conductor 30 for effecting the operation of relay ST, Fig. 12, and at armature msZ maintains earth on the motor start conductor 16 which was originally applied at armature al, Fig. 7, to set in operation the ringing and tone equipment, which in addition to other functions applies earth pulses at intervals of 9 seconds to the S pulse conductor 17 by the agency of the spring set and associated cam S, Fig. 14. Relay ST on operating at armature stl opens the homing circuit of the driving magnet DM of the delayed alarm rotary switch DAR, Fig. 12,. and at armature st2 prepares the circuit of relay PS, Fig. 12, for the reception of pulses received over the conductor 17 from the spring set and cam S.

Assuming now that the calling subscriber fails to dial before the reception of the first pulse after the operation of relay ST, relay PS will be allowed to operate its make-first armature ps1 over its left-hand winding and to operate its remaining armatures over both its windings in series at the cessation of the earth pulse; at armature ps2 relay PR is connected to conductor 17 so that on the reception of the next earth pulse relay PR operates. Relay PR at armature prl allows relay PM to operate and this relay at armature pml prepares the circuit of the driving magnet DM of the rotary switch DAR. Upon the cessation of the earth pulse, relay PR releases, and at armature prl breaks the circuit of relay PM and completes the circuit of the magnet DM. Relay PM is slow to release due to the presence of the copper slug fitted onto the heel end of its core and keeps armature pml operated for a period sufficient to ensure the correct operation of the magnet Dlvl. The magnet DM is therefore fully energized upon the release of relay PM and steps the wipers of the rotary switch DAR to the next set of bank contacts. Each succeeding pulse ap plied to conductor 17 by the S pulse cam will cause the wipers to be stepped on in like manner until that contact is reached to which conductor 18 is connected, in this case after four steps have been taken. Earth from the wiper lb is now transmitted along conductor 18 to operate relay ZP, Fig. 2, over its lower winding, via operated armature sp2. Relay ZP at armature zpl breaks the holding circuit of relay H to the line finder, Fig. 2, and at armature ap2 disconnects conductor 13, thus allowing relay LR, Fig. l, to release. Relay CO which was energized in series with relay LR being slow to release will remain held over the circuit including the subscribers instrument when relay LR releases, via resting armature 1T3, operated armature e03, subscribers line and instrument, resting armature Zr2 to earth. Earth is new extended over conductor 20 via operated armature e03, resting armature 173 and the supervisory lamp LP common to the group of subscribers line circuits to which this particular line circuit belongs, to operate relay LA, Fig. 11. Relay LA in operating at armature Za'l applies earth to conductor 21 to originate a supervisory alarm, the operation of which will be described later.

Returning now to the finder, relay H in releasing breaks the connection to the local first selector at armatures h3 and IL7 so that relay 2A in the latter switch will restore and when relay 2B has consequently restored due to the restoration of armature 2a1 earth from resting armatures 1h3 and 2041, winding of relay 2C, and resting armature 2123 will be connected to conductor 22 and then via the busy and test jack BTJ, Fig. 2, operated off-normal springs 1N1 of the finder switch to operate the release magnet lZ of the finder switch in series with relay IRA, Fig. 12, over conductor 98. If due to any fault, such as a mechanical defect or the like, correct release of the finder switch does not take place, relay lRA will remain operated and give an alarm in a manner shortly to be described. Assuming, however, that no such defectexists the finder switch and the local first selector will fully restore to normal. It should be pointed out that while the PG condition exists in the calling subscribers line circuit his line is busied on the final selector banks by earth from resting armature Zr2, resting armature bdl, circuit including the subscribers instrument, resting armature bd2, operated armature e02, resting armature Zr3, lower winding of relay LR, private normal conductor 12 to the final selector bank multiple. The busy relay 3G in the final selector, Fig. 4, is designed to operate in an extension of this circuit, while its resistance is of such a magnitude as to prevent the operation of relay LR over its lower winding in this circuit.

Considering now the case in which he calling subscriber dials before the reception of the first S pulse, he will have been receiving dial tone from earth, left-hand winding of dial tone transformer DTT, Fig. 13, conductor 99, normal position of llth step cam springs 1S1, lower windins. of relay 2A, resting armature lhl, conductor 32, operated armature k3, wiper 2a and bank con tact of finder switch, conductor 25, resting armature bdl, subscribers line and instrument, resting armature M2, conductor 2%, bank contact and wiper la of finder switch, upper winding of relay 1M, operated armature 7L7, conductor 31, resting armature lhZ, upper winding of relay 2A to battery, and when he dials relay 2A will impulse over this circuit and step the vertical magnet 232M in the well-known manner. It is considered necessary to describe only the digit absorbing function of this selector as apart from this fea ture the circuit is of the well-known group selector type employing break rotary interrupter springs 2R. By adjusting the normal post springs NPl and N1 2 tov operate on a certain level this switch is rendered capable of absorbing the digit associated with that level. Relay 2G, Fig. 3, will release when springs NPl break so that when relay 2C restores a circuit is completed for the release magnet 22M of this selector as follows: earth, resting armature 201, operated normal post springs resting armature f2, operated offnornial springs 2N2, release magnet 22M to battery via conductor 33 and relay 2RA, Fig. 12, so that the switch shaft is restored to normal. The release magnet in operating the release magnet springs ZZ ensures the continuation of this circuit until the off-normal springs 2N2 are opened. When the l tter springs break relay F operates over its lower winding in a circuit extending from earth, operated release magnet springs 25, resting armature f2, lower winding of relay F, operated armature 2hr), winding of release magnet ZZlVl, conductor 33, winding of relay 2RA, Fig. 12, to battery. The release magnet springs 2Z are adjusted to have a long stroke so that they remain closed for a period sufficient to allow relay F to operate its make first armature f1, whereupon it will operate fully over its upper winding in a circuit extending from: battery, upper winding of relay F, operated armature f1, operated armature 2B1 to earth. At armature f2 the release magnet circuit is opened to enable the shaft to he stepped upon the reception of the next series of impulses. It should be pointed out that due to the operated armature 3 short circuiting springs N'Pl the switch will not be forcibly released again should the same digit be dialled a second time. In this case relay 2G will remain operated after the cessation of vertical impulses so that when relay 2C restores the rotary magnet ZRM will operate over a circuit extending from battery, winding of rotary magnet ZRM, operated armature 2g2, resting contacts of armature 202, operated armature 2291, to earth in order to cutin the wipers and'tobreak the circuit of relay 2G at rotary interrupter springs. 23. Rotary hunting motion will then take place in the manner well-known to those skilled in the art until a free final selector, Fig. 4, isfound, whereupon relay 1H of the local first selector will operate in series with relay 26, since it is no longer shunted by the busying earths encountered by wiper 3c in. passing over the private contacts of engaged final selectors. and at o erated armatures lh 1712 will pre pare the circuit extending over conductors 35 and 35 of relay 3A of the combined regular and toll final selector, Fig. l, which has just been seized.

Relay 3A will thereupon operate in series with the subscribers line and instrument via resting contacts of armatures and de in series with the windings of relay All which are connected in opposition to each other so that relay AA cannot operate in this circuit. Relay 3A in operating at armature Sal completes circuits for relays 3B and the circuit of the. latter relay extending over off-normal springs Bl il, resting armature cl, and upper winding of the relay to battery. At 3hl and Sol a circuit is prepared for the vertical magnet 3V1Vl of the final selector over the lower winding of relay 30 while at armature 3B2 earth is applied to the release trunk conductor 3'7 to guard the final selector and also to hold relay ll-l in the local first selector, relay 1-1 in the finder switch relays LR and CO in the subscribers line and cut -off circuit. At armature the motor start conductor 16 is earthed via resting armature lf l. At the first interruption the calling partys relay 3A restores but relay 31% remains operated by virtue of its heel end slug and a circuit is now completed from earth, resting armature 3:11, operated armature 3221, operated armature 3c1, lower winding of re lay 3C, resting armature e2, winding of vertical magnet BVM to battery. The vertical magnet 3VM therefore lifts the shaft and wipers to the first level thus allowing the off-norrnal springs 3N1 to break the original operating circuit of relay 3C which however remains operated throughout the train of impulses which follow due to the impulse currents in its lower winding as it is pro vided with a slug fitted on the heel end of its core. Subsequent impulses re-act on the vertical magnet BVM in a similar ni 1er to the first, and the shaft and wipers are th tore stepped to the required level, relay f, restoring after the completion of the last impulse and preparing the circuit of the rotary magnet Re ay 3A responds to the final series of impulses d led by the calling party and transmits impulses over the following circuit: earth, resting armature 354i, operate-J armature 3221, resting armatures Sci, 3g2, 2533, M2, 22 2 and i023, winding of rotary magnet BRM to battery. Relay E operates over its upper wind ing in parallel with the rotary magnet 312M and at operated armature e2 short-circuits its own lower winding, this having the effect of a heel end slug relay E is thus enabled to remain operated throughout the train or impulses. Relay on operating, at armature 63 short circuits armatures 2tb3, 3g2 and Sci. so that any subsequent operation of relays 2TB, 3G or 3C due to the wipers of the final ector passing over engaged contacts, or due to other causes which will hecome apparent later, will not 1" suit in the clipping of the pulses. The wipers 103 to 6d of l final selector are thus stopped to the required line.

Considering now the case in which the required subscriber is engaged on another call, wiper 3d will encounter earth on the associated hank contact and owing to the fact that relay E remains operated for an instant after wiper 3d has reached the contact, relay 36 will now operate from battery, winding of relay 3G, resting armature m1, operated armatures 3b3 and ed, resting contacts of armature 2713, resting armatures 225212 and m2, wiper 3d and bank contact associated with called subscriber, conductor 38, operated armature llrl in called subscribers line and cutoff circuit, Fig. 5, to the release trunk conductor 39 which is earthed by a selector or final selector in the train of switches in use for the call upon which the called subscriber is engaged. It should be mentioned that in certain conditions, for instance when the called subscriber is busied on a permanent loop condition (which has already been described) the wiper 3d may not encounter a full earth and for this reason relay 3G is fitted with a lightly tensioned make-first armature 391 which relay 3G may operate even on a high resistance earth. When relay E restores, however, relay 3G operates fully over a circuit extending from: earth, operated armature 3b2, operated armature 391, resting armature drl, resting contacts 0f armature e4, operated armature 3b3, resting armature m1, winding of relay 3G to battery and at armature 3g2 disconnects the impulsing circuit of the rotary magnet SRM so that further dialling will not anect the latter while at armature 3173 relay 3G applies busy tone, which may be a high pitched tone interrupted at short regular intervals, from conductor 40 via resting armatures (Z12 and c5, speaking condenser Q13 and thence to the calling subscriber via the calling switch train.

It should be pointed out here that the equipment utilized in the generation and distribution of ringing and the various tones required in the working of the system, Fig. 14, is substantially the same as that described in British Patent No. 351,549. It is not intended, therefore, to describe this in detail, and furthermore in order -to avoid undue complication of the drawings certain conductors utilized in the transmission of tones and the like have not been shown extended to the ringing and tone circuit, Fig. 14,

although it should be understood that these conductors actually do extend thereto.

When the calling subscriber hears the busy tone he must thereupon hang up his receiver and, if he wishes, recall after an interval. Upon the removal of the direct current circuit from across conductors 35 and 36 consequent upon the calling subscriber restoring his receiver relay 3A will restore and allow relay 33 to restore after its slow release period. The release magnet will now operate over a circuit extending from: earth,

resting armatures 3:11, 3bl, d1, operated offnormal springs 3N1, winding of release magnet 32M, conductor 41, winding of release relay BRA, Fig. 12, to battery and will therefore cause the shaft and wipers of the final selector to restore to normal, whereupon the circuit of the release magnet 32M will be opened when springs 3N1 break. The removal of earth from conductor 37 consequent upon the restoration of armature 3272 will enable relay 1B. of the local first selector to restore and complete the release magnet circuits or" the selector and also of the finder switch associated with it, both switches thereupon restoring to normal. Relays LR and CO in the subscribers line and cut-off circuit are also al itor wipers reach the correct set of bank contacts so that when relaly E' restores a circuit will be completed for relay 2H of the final selector over a circuit extending from: earth, operated armature 3b2, resting armature 3g1, lower Winding of relay 2H, resting armature e4, resting contact oi armature 2h3, resting armatures 2tb2 and m2, wiper 3d, bank contact, conductor 38, lower winding of relay lLR, winding of relay 100 to battery. Relay 21-1 is enabled to operate its make first armature 2h1 over this circuit so that it will then look up over its upper winding to earth via the operated armature 2h1 and operated armature 3b l. Relay 2H in operating at armatures 2/14 and 2h5 completes the ringing circuit extending from ring-return battery on conductor 52, resistance YA, resting armature 1;2, operated armature 2h5, resting armature tdd, wiper 2d and bank contact, conductor 42, resting armature 112112, called subscribers line and calling device, resting armature lbdl, conductor 43, bank contact and wiper 1d, resting armature td5, operated armature 53b4, resting armature 1 3, right-hand winding of relay 1F to earthed interrupted ringing applied to conductor 42. Full earth is also extended to wiper 3d over resting armature 0M3, operated armature 2713 and resting armatures 2tb2 and m2 in order to busy the called subscriber.

The importance of the fact that a full and not a resistance earth is connected when the calling party not a toll operator will be appreciated later. Ring back tone which is in effect an echo of the ringing is transmitted back to the calling subscriber from interrupted ringing conductor 42, right-hand winding of relay 1F, resting armature 1 3, operated armature 27b6, ring-back tone condenser QC, speaking condenser QA, conductor 35, and so out to the calling subscriber to inform him that the wanted subscribers bell is being rung.

When the called subscriber replies in answer to the ringing the resultant direct current circuit across the conductors 42 and 43 will cause relay IE to operate its make first armature 1]1 over its right-hand winding and then operate fully over its left-hand winding via operated armatures 1 fl and 3%. Relay 1F in operating at armature 1f4 removes earth from the motor start conductor 16 and at armatures U2 and U3 cuts off ringing and switches through the called subscribers circuit. Due to the operation of armature 1]2, relay D energizes over its right-hand winding and at armatures 113 and d4 reverses current in the calling subscribers circuit in order tometer the call. This is accomplished due to the operation of the meter relay 1M in the line finder circuit, Fig. 2. The lower winding of relay 1M, serving as a polarizing winding, will have been energized via an operated armature he of the line finder but until the calling party replies current in the upper or line winding will have been flowing in the wrong direction for the operation of relay 1M. Upon current being reversed, however, relay lIVI operates and at armature lml provides earth in order to operate the calling subscribers meter to register the call over a circuit extending from earth, operated armatures lml and b4, wiper 4a and bank contact of finder switch, conductor 44, operated armature e04, winding of subscribers meter MTR to battery. The meter operates, thus registering the call and locks up via its operated armature mtrl and operated armature co l.

Returning now to the final selector, relay D at armatures all and (12 also prepare circuits which will come into operation in the event of the calling subscriber clearing before the called subscriber at the conclusion of the call. If this occurs relay 3A will restore, and during the slow release period of relay 3B, relay E will operate over its original operating circuit. The rotary magnet 38M is, however, prevented from operating over this circuit by the operated armature 2h2. Since relay ll is a slow release relay by virtue of its lower winding being short-circuited at operated armature e2, it will remain operated for a short period after relay 33 has restored, and at operated armature e4 will disconnect conductor 37 from the source or earth at resting armature dr3, thus allowing the preceding switch train to restore to normal. Upon the restoration of relay E, however, earth will again be extended via resting armature dr3, operated armature 2h3, resting armatures 3276 and 64, low resistance lower winding of relay 2H, resting armature 3g1, conductor 37, in order to re-guard the final selector against seizure by another selector until the called party has hung up his receiver. Relays 1F and 2H will still remain operated via operated armatures C12 and lf4 to earth, and a circuit is also completed for the final selector supervisory lamp lLP from earth, resting armatures al and 3121, operated armature d1, supervisory lamp lLP, conductor '19, winding of relay ILA, Fig. 13, to battery. Relay ILA in operating at armature llcl closes a circuit for relay in extending from battery, lower winding relay 4A, operated armature ilal, resting armature 4121, home contact and wiper 2c of delayed alarm rotary switch DBR to earth, whereupon relay 4A locks up in a circuit extending from: earth, operated armature 1Za2, supervisory lamp 2LP, common to a group of final selectors upper winding of relay 4A, operated armature 4al, upper winding of relay 43 to battery. Due to the comparatively high resistance of the upper winding of relay 4A, relay 413 will not be operated in this circuit nor will the supervisory lamp 2L? light. Relay m also at armature 4:12 prepares a circuit for the lower winding of relay 4B and at armature closes a circuit for relay 1ST. The delayed alarm rotary switch DBR will now proceed to step its wipers around under the control of relays lPR and 1PM in an exactly similar manner to the delayed alarm rotary switch DAR, Fig. 12, previously described. In this case, however, assuming the called subscriber continues to hold the final selector, the rotary switch makes 20 steps being equivalent to a delay period of three minutes before relay 43 operates over its lower winding via operated armature 4.-a2, bank contact and wiper 1e of rotary switch DBR, to earth and by short-circuiting the looking or upper winding of relay 4A at operated armature 432 causes the latter relay to restore and break the circuit of relay 1ST which thereupon releases and completes the homing circuit of the driving magnet lDM of rotary switch DER over a circuit extending from: battery, winding rotary magnet lDM, magnet interrupter springs ldm, resting armature lstl, commoned bank contacts and wiper ie of rotary switch DBR to earth. The operation of armature 4112 in addition to causing the release of relay iA also enables the supervisory lamp 2LP to light since the upper winding of relay 4B is of comparatively low resistance, relay 4B meanwhile energizing in the same circuit. Relay 4B at armature 4213 provides earth to light the supervisory lamp BLP this being the main supervisory lamp for the rack upon which the particular final selector is mounted.

Considering again the final selector, Fig. 4, when the called subscriber hangs up his receiver the consequent release of relay D will complete a circuit for the release magnet 3Zlvl via resting armature d1, while at the same time the operating circuit or relay ILA, Fig. 13, is broken, resulting in the release of the supervisory equipment assuming that it is not being held by any cher switch in the same condition.

In the event of the called party hanging up before the calling party relay D will restore but relay will remain held by the calling party and retain relay 3B which will in turn hold relays 1F The switch supervisory lamp 1L? will now glow over a circuit extending from: earth, operated armature lie, resting armature d2, lamp lLi to battery via relay ILA as before described.

thus described the operations which take place in the various switches in the train when a call initiated by a subscriber, it is now proposed to describe the additional operations brought into use when a toll operator utilizes the final selector for the purpose of offering a toll call to a subscriber. The toll operator is given direct access to an incoming or toll selector,

Fig. 8, by inserting the plug of her cord circuit into a jack JK, Fig. 11, which connects via conductors 45 and 46 with relay 5A, Fig. 8, of the toll selector, and by operating the ring and dial key RDH she is enabled to dial onto this selector and thereby operate the same. A detailed description of the operation of this switch is not necessary since apart from the fact that it does not possess a digit absorbing feature its functions are exactly similar to those of the local first selector, Fig. 3, already described. It should be pointed out that this particular group selector has been designed to enable it to be used when required in conjunction with a finder switch such as that shown in Fig. 2 and already described. In this case conductors 22a, 26a, 27a and 29a would be conn cted to conductors 22, 26, 27 and 29 respectively of the finder switch.

Assuming now that the toll operator, by manipulating the dial DL associated with her position has operated the toll selector, the latter will hunt for and seize a free combined regular and toll final selector in the well-known manner. As soon as the toll selector has switched, relay EA will operate but this time relay AA will also operate since in the normal position of the operators dial DL earth is connected to both speaking conductors through the shunt springs DLS of the dial. The differential eiiect oi the winding of relay AA will, therefore, not now apply, and the relay will operate due to current in its upper winding alone. At armature ml a circuit is closed for relay AD which will operate and complete a circuit at armature ads for relay DR which looks up to earth at operated armature 3194 via its own operated armature dre. The operator now dials and relay AA will restore as soon as the dial is moved off normal since current will once more flow in opposition in its two windings. Relay AA in restoring will release relay AD. The operation of the vertical and rotary magnets of the final selector takes place in a similar manner to that already escribed except that during the rotary motion relay 3C re-operates in a circuit extending from: earth, operated armatures dr3 and c1, upper winding of relay SC to battery. It should be noted 

